1. Field of the Invention
This invention relates to xerography and more particularly to a method of removing toner deposits from a photosensitive drum in a xerographic copying machine.
2. Description of the Prior Art
One of the most popular printing or copying technology nowadays is xerography in which an electrostatic latent or negative image corresponding to an original print to be copied is formed on an electrically charged layer of a photosensitive material such as selenium provided on a rotary drum and then an oppositely charged toner in the form of a resinous powder is electrostatically adsorbed onto and tones the latent image which is finally transferred onto a print paper through the medium of heat. The conventional xerography process suffers from the problem that the toner is difficult to transfer in its entirely to the print paper, resulting in a portion of the toner remaining on the drum. It has been a common practice to scrape the residual toner off the drum by pressing a blade of a synthetic resin such as polyurethane against the drum.
FIG. 6 of the accompanying drawings schematically illustrates a typical xerographic copying machine 1 in which exposing, developing and transferring are carried out in this order as a photosensitive drum 2 makes a full clockwise rotation in the direction indicated by an arrow. Light from a light source 3 is irradiated to the original 5 placed on a sheet of glass 4, and the light reflected therefrom is focused on the drum 2 by a bar lens 6. The copying machine 1 is designed to move the original 5 relative to the light source 3 and the lens 6 in synchronism with the rotation of the drum 2, whereby the photosensed or exposed areas of the original are formed to appear as an inverted latent image on the drum 2. The exposed image on the drum 2 is developed on a developer drum 8 by a toner from a reservoir 7 and then moved to a transfer station 11 where a print paper supplied from a cartridge 9 is pressed against the drum 2 to pick up the developed image. Subsequently, the transferred image is fixed or settled on the paper as the latter is pressed on opposite sides by a heat roller 13 and a pressure roller 14. The paper is thereafter discharged out of the copying machine 1 onto a tray 16 by the heat roller 13 and the pressure roller 14. The toner that has been deposited on the pressure roller 14 during image fixation is removed by a cleaning roller 17.
In the meantime, the portion of the toner that has been left during the transfer process on the drum 2 is scraped off by the blade 18 and placed in a collector 19. However, to ensure complete removal of the residual toner, the blade 18 must have a scraping edge of a high degree of precision and hence is expensive to manufacture. Furthermore, because the blade 18 must be pressed against the drum 2 with great physical force, the blade edge tends to wear out rapidly due to friction and is otherwise vulnerable to damage on contact with foreign matter such as dust jammed between the blade edge and the drum surface.